When overwriting already allocated blocks, f2fs_iomap_begin() calls
f2fs_overwrite_io() to check block mappings. However,
f2fs_overwrite_io() iterates through all mapped blocks in the range,
which can be inefficient for fragmented files with large I/O requests.

This patch optimizes f2fs_overwrite_io() by adding a 'check_first'
parameter and introducing __f2fs_overwrite_io() helper. When called from
f2fs_iomap_begin(), we only check the first mapping to determine if the
range is already allocated, which is sufficient for setting
map.m_may_create.

This optimization significantly reduces the number of f2fs_map_blocks()
calls in f2fs_overwrite_io() when called from f2fs_iomap_begin(),
especially for fragmented files with large I/O requests.

Fixes: 351bc761338d ("f2fs: optimize f2fs DIO overwrites")
Reviewed-by: Sungjong Seo <sj1557.seo@samsung.com>
Reviewed-by: Sunmin Jeong <s_min.jeong@samsung.com>
Signed-off-by: Yeongjin Gil <youngjin.gil@samsung.com>
---
 fs/f2fs/data.c | 10 ++++++++--
 1 file changed, 8 insertions(+), 2 deletions(-)

diff --git a/fs/f2fs/data.c b/fs/f2fs/data.c
index 2e133a723b99..bfbd717e628a 100644
--- a/fs/f2fs/data.c
+++ b/fs/f2fs/data.c
@@ -1851,7 +1851,8 @@ int f2fs_map_blocks(struct inode *inode, struct f2fs_map_blocks *map, int flag)
 	return err;
 }
 
-bool f2fs_overwrite_io(struct inode *inode, loff_t pos, size_t len)
+static bool __f2fs_overwrite_io(struct inode *inode, loff_t pos, size_t len,
+				bool check_first)
 {
 	struct f2fs_map_blocks map;
 	block_t last_lblk;
@@ -1877,6 +1878,11 @@ bool f2fs_overwrite_io(struct inode *inode, loff_t pos, size_t len)
 	return true;
 }
 
+bool f2fs_overwrite_io(struct inode *inode, loff_t pos, size_t len)
+{
+	return __f2fs_overwrite_io(inode, pos, len, false);
+}
+
 static int f2fs_xattr_fiemap(struct inode *inode,
 				struct fiemap_extent_info *fieinfo)
 {
@@ -4443,7 +4449,7 @@ static int f2fs_iomap_begin(struct inode *inode, loff_t offset, loff_t length,
 	 * f2fs_map_lock and f2fs_balance_fs are not necessary.
 	 */
 	if ((flags & IOMAP_WRITE) &&
-		!f2fs_overwrite_io(inode, offset, length))
+		!__f2fs_overwrite_io(inode, offset, length, true))
 		map.m_may_create = true;
 
 	err = f2fs_map_blocks(inode, &map, F2FS_GET_BLOCK_DIO);
-- 
2.43.0

On 1/16/2026 6:23 PM, Yeongjin Gil wrote:
> When overwriting already allocated blocks, f2fs_iomap_begin() calls
> f2fs_overwrite_io() to check block mappings. However,
> f2fs_overwrite_io() iterates through all mapped blocks in the range,
> which can be inefficient for fragmented files with large I/O requests.
> 
> This patch optimizes f2fs_overwrite_io() by adding a 'check_first'
> parameter and introducing __f2fs_overwrite_io() helper. When called from
> f2fs_iomap_begin(), we only check the first mapping to determine if the
> range is already allocated, which is sufficient for setting
> map.m_may_create.
> 
> This optimization significantly reduces the number of f2fs_map_blocks()
> calls in f2fs_overwrite_io() when called from f2fs_iomap_begin(),
> especially for fragmented files with large I/O requests.
> 
> Fixes: 351bc761338d ("f2fs: optimize f2fs DIO overwrites")
> Reviewed-by: Sungjong Seo <sj1557.seo@samsung.com>
> Reviewed-by: Sunmin Jeong <s_min.jeong@samsung.com>
> Signed-off-by: Yeongjin Gil <youngjin.gil@samsung.com>
> ---
>   fs/f2fs/data.c | 10 ++++++++--
>   1 file changed, 8 insertions(+), 2 deletions(-)
> 
> diff --git a/fs/f2fs/data.c b/fs/f2fs/data.c
> index 2e133a723b99..bfbd717e628a 100644
> --- a/fs/f2fs/data.c
> +++ b/fs/f2fs/data.c
> @@ -1851,7 +1851,8 @@ int f2fs_map_blocks(struct inode *inode, struct f2fs_map_blocks *map, int flag)
>   	return err;
>   }
>   
> -bool f2fs_overwrite_io(struct inode *inode, loff_t pos, size_t len)
> +static bool __f2fs_overwrite_io(struct inode *inode, loff_t pos, size_t len,
> +				bool check_first)

Yeongjin,

You may missed to add logic related to check_first parameter?

Thanks,

>   {
>   	struct f2fs_map_blocks map;
>   	block_t last_lblk;
> @@ -1877,6 +1878,11 @@ bool f2fs_overwrite_io(struct inode *inode, loff_t pos, size_t len)
>   	return true;
>   }
>   
> +bool f2fs_overwrite_io(struct inode *inode, loff_t pos, size_t len)
> +{
> +	return __f2fs_overwrite_io(inode, pos, len, false);
> +}
> +
>   static int f2fs_xattr_fiemap(struct inode *inode,
>   				struct fiemap_extent_info *fieinfo)
>   {
> @@ -4443,7 +4449,7 @@ static int f2fs_iomap_begin(struct inode *inode, loff_t offset, loff_t length,
>   	 * f2fs_map_lock and f2fs_balance_fs are not necessary.
>   	 */
>   	if ((flags & IOMAP_WRITE) &&
> -		!f2fs_overwrite_io(inode, offset, length))
> +		!__f2fs_overwrite_io(inode, offset, length, true))
>   		map.m_may_create = true;
>   
>   	err = f2fs_map_blocks(inode, &map, F2FS_GET_BLOCK_DIO);

> On 1/16/2026 6:23 PM, Yeongjin Gil wrote:
> > When overwriting already allocated blocks, f2fs_iomap_begin() calls
> > f2fs_overwrite_io() to check block mappings. However,
> > f2fs_overwrite_io() iterates through all mapped blocks in the range,
> > which can be inefficient for fragmented files with large I/O requests.
> >
> > This patch optimizes f2fs_overwrite_io() by adding a 'check_first'
> > parameter and introducing __f2fs_overwrite_io() helper. When called
> > from f2fs_iomap_begin(), we only check the first mapping to determine
> > if the range is already allocated, which is sufficient for setting
> > map.m_may_create.
> >
> > This optimization significantly reduces the number of
> > f2fs_map_blocks() calls in f2fs_overwrite_io() when called from
> > f2fs_iomap_begin(), especially for fragmented files with large I/O
> requests.
> >
> > Fixes: 351bc761338d ("f2fs: optimize f2fs DIO overwrites")
> > Reviewed-by: Sungjong Seo <sj1557.seo@samsung.com>
> > Reviewed-by: Sunmin Jeong <s_min.jeong@samsung.com>
> > Signed-off-by: Yeongjin Gil <youngjin.gil@samsung.com>
> > ---
> >   fs/f2fs/data.c | 10 ++++++++--
> >   1 file changed, 8 insertions(+), 2 deletions(-)
> >
> > diff --git a/fs/f2fs/data.c b/fs/f2fs/data.c index
> > 2e133a723b99..bfbd717e628a 100644
> > --- a/fs/f2fs/data.c
> > +++ b/fs/f2fs/data.c
> > @@ -1851,7 +1851,8 @@ int f2fs_map_blocks(struct inode *inode, struct
> f2fs_map_blocks *map, int flag)
> >   	return err;
> >   }
> >
> > -bool f2fs_overwrite_io(struct inode *inode, loff_t pos, size_t len)
> > +static bool __f2fs_overwrite_io(struct inode *inode, loff_t pos, size_t
> len,
> > +				bool check_first)
> 
> Yeongjin,
> 
> You may missed to add logic related to check_first parameter?
> 
> Thanks,
I made a mistake. I will resend the v2 patch.
Thank you for the review.
> 
> >   {
> >   	struct f2fs_map_blocks map;
> >   	block_t last_lblk;
> > @@ -1877,6 +1878,11 @@ bool f2fs_overwrite_io(struct inode *inode,
> loff_t pos, size_t len)
> >   	return true;
> >   }
> >
> > +bool f2fs_overwrite_io(struct inode *inode, loff_t pos, size_t len) {
> > +	return __f2fs_overwrite_io(inode, pos, len, false); }
> > +
> >   static int f2fs_xattr_fiemap(struct inode *inode,
> >   				struct fiemap_extent_info *fieinfo)
> >   {
> > @@ -4443,7 +4449,7 @@ static int f2fs_iomap_begin(struct inode *inode,
> loff_t offset, loff_t length,
> >   	 * f2fs_map_lock and f2fs_balance_fs are not necessary.
> >   	 */
> >   	if ((flags & IOMAP_WRITE) &&
> > -		!f2fs_overwrite_io(inode, offset, length))
> > +		!__f2fs_overwrite_io(inode, offset, length, true))
> >   		map.m_may_create = true;
> >
> >   	err = f2fs_map_blocks(inode, &map, F2FS_GET_BLOCK_DIO);